Abstract:

[Objective] This experiment was conducted to explore the effects of different initial water contents and co-fermentation with probiotics and protease on quality of soybean meal. [Method] ① A single factor experimental design was adopted to determine the optimal ratio of fermentation material to initial water. Five treatment groups with different initial water contents were set up, and the ratios of material to water were 1∶0.4, 1∶0.5, 1∶0.6, 1∶0.7 and 1∶0.8, respectively. There were three replicates for each treatment group. The compound probiotics （Bacillus subtilis∶yeast∶Enterococcus faecalis=1∶1∶1） were used as starter to ferment soybean meal, and the apparent characteristics, nutritional indicators and living bacteria contents of the fermented soybean meal were assessed. ②A single factor experimental design was used to set up five treatment groups with different neutral protease addition amount of 0, 100, 200, 400 and 800 IU/g. Each treatment group had three replicates. The apparent characteristics, nutritional indicators, live bacteria contents, and protein subunit distribution of the fermented soybean meal were further analyzed to determine the optimal neutral protease addition amount. [Result] ①There was no significant （P=0.074） difference in crude protein level of the fermented soybean meal with varied ratios of material to water. The highest crude protein level of the fermentation product was observed when the ratio of material to water was 1∶0.6, which was elevated by 9.39% compared with the soybean meal before fermentation. With the increase of initial water content of the fermentation system, the pH value of fermented soybean meal was decreased significantly （P<0.01）, while the content of lactic acid and the survival amount of the three species of microbes in the compound probiotics were elevated significantly （P<0.01）. The content of lactic acid after fermentation in 1∶0.6 treatment group was significantly （P<0.05） higher than that in 1∶0.4 and 1∶0.5 treatment groups. The survival amount of the three species of microbes in the compound probiotics was the highest when the ratio of material to water was 1∶0.8, with the total amount reached 1.43×10⁹ CFU/g. Considering the industrial production conditions with the above results, the optimal ratio of material to water for the subsequent experiment was determined as 1∶0.6.②With the ratio of material to water at 1∶0.6, different protease addition levels had no significant （P>0.05） effect on the crude protein content of fermented soybean meal. However with the increase of protease addition amount, the proportion of small molecular proteins in fermentation product increased linearly. In the treatment group with protease addition of 800 IU/g, the proportion of proteins with molecular weights less than 30 kDa was as high as 65.56%, which was 2.61 times higher than that in the group without protease addition. The survival amount of the three species of microbes in the compound probiotics was decreased with the increase of protease addition amount. The survival amount of Bacillus subtilis and Enterococcus faecalis in 100 IU/g treatment group was extremely significantly （P<0.01） higher than that in 200, 400 and 800 IU/g treatment groups, and that of yeast was extremely significantly （P<0.01） higher in comparison to 400 and 800 IU/g treatment groups. [Conclusion] The quality of soybean meal can be effectively improved by a co-fermentation with addition of compound probiotics and 100 IU/g neutral protease in the substrates at a ratio of material to water of 1∶0.6.

Key words: fermented soybean meal, probiotics, protease, production technology